Structural analysis of potassium borate solutions.
Phys Chem Chem Phys
; 25(17): 12207-12219, 2023 May 03.
Article
em En
| MEDLINE
| ID: mdl-37092350
ABSTRACT
In this work, H/D isotopic substitution neutron diffraction was combined with empirical potential structure refinement (EPSR) and DFT-based quantum calculations to study the interactions between B(OH)3 boric acid molecules, B(OH)4- metaborate ions, water molecules, and potassium cations in borate solutions. The results show that the solute ions and molecules have a marked effect on the second coordination shell of the water molecules, causing a greater deviation from a tetrahedral structure than is observed for pure water. Potassium ions and trans-B(OH)3 tend to form a monodentate contact ion pair (MCIP) with a K-B distance â¼3.8 Å, which remains constant upon changing the solution concentration. Potassium ions and cis-B(OH)3 form both a MCIP at K-B â¼3.8 Å and a bidentate contact ion pair (BCIP) at K-B â¼3.4 Å. As the solution concentration increases, there is a BCIP to MCIP transformation. Boric acid molecules can undergo hydration in one of three ways direct hydration, interstitial hydration, and axial hydration. The energetic hydration preference is direct hydration â interstitial hydration â axial hydration. Nine water molecules are required when all water molecules directly interact with the -OH groups of B(OH)4-, and a tenth water molecule is located at an interstitial position. The hydrogen bonding between boric acid molecule/metaborate ion and water molecules is stronger than that between water molecules in the hydration layer.
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MEDLINE
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2023
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Article